1. Field of the Invention
This invention relates to a wide field of view high numerical aperture lens systems with partial color correction for use in projection televisions and, in particular, in projection televisions employing cathode ray tubes (CRTs).
2. Description of the Prior Art
Prior art projection lenses for CRT projection televisions have comprised, from the long conjugate to the short conjugate, a weak aspherical corrector followed by a strong positive power unit, another weak aspherical corrector, and a strong negative power element in close proximity to the CRT. A description of this lens configuration can be found in a number of prior patents, including Betensky, U.S. Pat. No. 4,697,892, and Moskovich, U.S. Pat. Nos. 4,682,862, 4,755,028, and 4,776,681.
To achieve correction of chromatic aberrations, a color correcting doublet is often included in the strong positive power unit. U.S. Pat. No. 4,963,007 describes a lens configuration where color correction is achieved by adding negative power, high dispersion elements to both front units. In these lens forms, the glass elements and the shape of the plastic elements have resulted in higher manufacturing costs.